The 850-page report into the collapse of MG Rover will finally be published today, more than four years after the £16.3m investigation began. It is understood that the report will heavily criticise the Phoenix Four, the businessmen who owned the car manufacturer when it went bust with the loss of 6,500 jobs in April 2005.

Together with Rover's former chief executive Kevin Howe they paid themselves more than £40m in pensions and salaries after they bought the company from the German motor manufacturer BMW for a token £10 in 2000. The workers' pension fund ended up £470m in deficit and many employees had their payouts slashed as a result. The German manufacturer – which had nicknamed the lossmaking MG Rover "the English patient" – also provided a dowry of £427m to the Phoenix Four to take it off their hands.

The four, John Towers, Peter Beale, John Edwards and Nick Stephenson, have denied any wrongdoing, and will not face criminal proceedings. They could, however, be barred from being directors of companies.

The government is unlikely to escape criticism for its role in the affair. Ministers backed the takeover in 2000 in preference to a rival bid from the private equity firm Alchemy Partners, thinking it would safeguard more jobs. The government also lent the Longbridge carmaker £6.5m in a doomed attempt to keep it afloat, months before the general election in May 2005. It also prepared a £100m bridging loan, but withdrew this at the last minute in 2005.

The government has been criticised for delaying publication of the report, including by the local Labour MP MP Richard Burden, but ministers at the time insist they made the right decisions to try to save the company. Both Gordon Brown and the former Industry Secretary Stephen Byers will be hoping they are not directly criticised in the report. Some of those involved refused to comment ahead of publication this morning But they are braced for criticism that they failed to monitor the state of the firm and brought forward its demise by announcing it was in need of further loans in 2005.

Ministers were accused of trying to ensure the company's collapse came at the start of the 2005 election campaign and not before. The industry secretary at the time Patricia Hewitt always denied the charge, arguing the firm's need for a bridging loan had to be made public.

Lord Mandelson the current business secretary is likely to argue that the report is largely historic and pales into insignificance alongside the trauma of the Vauxhall car plants in England currently under threat due to the collapse of General Motors. He will also seek to deflect criticism of the government by arguing it has taken the stiffest action possible against the directors at the time given they have not broken company law.

The trade union Unite representing the workforce will demand maximum compensation and will direct the bulk of its ire at the four directors. Rover was the last large independent British car manufacturer. It is now owned by a Chinese state owned company, SAIC, which employs a few hundred at the Longbridge site and has shipped much of the tools and equipment to China.

Accountants BDO Stoy Hayward and the government-appointed inspectors Guy Newey QC and Gervase MacGregor led the investigation. The taxpayers' bill for the investigation stood at £16.3m at the end of July, making it one of the longest and most expensive forensic investigations into a failed business in British history.

The business secretary, Lord Mandelson, was criticised last month after he passed the inspectors' report to the Serious Fraud Office, which would have prevented its publication until after next year's general election. But the SFO decided not to launch a criminal investigation, allowing the report to be published.